just a heads up, there is no such thing as a 40a 18650. its more likely that your battery didnt make it into a 'a' grade batch from a major manufacturer, and was sold for cheap to whatever shady company put that 40a label on it (and put you in danger). we cant tell you if its safe or not because we dont know the actual rating of your battery. you are using a regulated device, so that should offer a layer of protection, but some of those re-wrapped batteries are terribly over rated (it could be a 10a battery from what i have seen in the past), so i suggest you try to get some authentic sony/samsung/lg batteries from a place like liion-wholesale or imr-batteries. a good choice right now are the sony vtc series. on a regulated device the vtc6 is a great choice, and the new vtc6a look even better. stay safe
ps - look up battery mooch, hes our battery saint in the vape community, who tests the batteries to verify the stats on the wraps and keeps us all safe.
he has videos on youtube that will help you get a good start on battery knowledge, and he posts detailed charts and info on battery performance on his blog. it doesnt matter if you have an expensive mod and artist crafted coils when you are using junk batteries. they are literally the foundation of a good/safe vape.